The cutting end of most CNC machines has either a consumer-grade router or a spindle.
Routers are very commonly used in hobby CNCs and some of the most popular ones are Makita RT0701C, DEWALT DWP611, and Bosch PR20EVS.
Spindles pack more power and are VFD controlled most often.
The most popular spindles used by CNC hobbyists are made in China like the Huanyang VFD Spindle.
Which among the two do you really need and how are they different from each other?
The choice of cutting head depends on several factors like the material you intend to mill, the power you need, and also the overall rigidity of your CNC machine.
I go through every important difference between the two to help you understand which one you need.
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Speed Control- Router vs Spindle
Speed is one of the major parameters that should be considered while selecting a cutting tool for your production.
This is because different materials require different speeds to make smooth cuts.
Routers have a speed dial to adjust the speed manually and do not provide any feedback. You can plug it into any standard 120 V wall socket and start making cuts.
Typically, routers are designed to use small cutting bits, which require high RPM to keep the feed rate sufficient.
Routers are prone to bog down under heavy loads conditions, such as thick metal machining.
Hence, routers are suitable for woodworking, which requires a cutting speed of more than 16,000 RPM, and non-ferrous metal machining like aluminum, which requires a cutting speed lower than 20,000 RPM.
Although there are experts who cut steel with a router using adequate coolants and adaptive toolpaths, it's far from ideal.
Spindles require the use of a VFD (inverter), which adjusts the RPM, hence ensuring virtual speed control. This variable speed feature lets you work with large diameter bits if you are planning to use them in the future.
For instance, facing bits require a maximum of 8,000 RPM or lower, and variable spindle speed provides you good chip load and fine surface finish.
The variable speed feature of spindles offers high-speed for roughing operations and low-speed for surface finishing.
The low RPM of spindles provides them enough torque to cut non-ferrous metals like steel and tensile metals like titanium.
Additionally, high RPM of spindles offer you faster feed rates, longer bit life, and lower cycle times than routers. With this, you can work with veneer plywood, hardwood, aluminum, and plastics.
However, wrong VFD settings may damage your spindle, like spindle heating, even running unloaded, so make sure to match the spindle's voltage, current, and frequency rating with VFD.
Typically, an acceptable runout for CNC machining is 0.0002 inches.
Routers have significantly more runout than spindles, and it can considerably affect the cutting accuracy on workpieces.
Generally, new routers have runout of 0.0010" - 0.0015", which may degrade according to conditions of router bit bearings.
New spindles have runout of 0.0002" or less, and it is maintained for 3 - 4,000 hours, which is the life span of high-grade bearings used in spindles.
Hence, if your project can tolerate error margins, a router is an economical solution. For making precise cuts and smooth finishing, I recommend a spindle for your application.
Routers are louder than spindles, even under no-load conditions.
So if you are using your CNC router in a home setting, it might be better to choose a spindle just to keep the noise low.
However, the cutting action of bits is very loud on both, so make sure to put your ear protection on, whether working with a router or a spindle.
Cooling-Water Cooled/Air Cooled
Mostly high-powered spindles are water-cooled, which use distilled water to provide proper cooling.
Spindles with small motors like 2 hp are air-cooled and offer more torque than water-cooled spindles due to their design.
If you want to use spindles for a prolonged period, even a whole day, I suggest using water-cooled spindles because water has a higher heat capacity than air. Hence they can run continuously to provide good cutting accuracy.
Additionally, water-cooled spindles are much quieter compared to air-cooled spindles.
A major problem in water-cooled spindles operation is a cold-weather condition because it prevents spindles from running, so you have to consider it as well.
All routers use an air-cooling mechanism, as they don't have water cooling options.
Hence, they do not require any external device support like water pumps and storage tanks, which are essential for water-cooled spindles.
So if you are a hobbyist and work intermittently on your CNC router, a router is an acceptable choice.
I have noticed that most routers are advertised with "peak" horsepower as a power rating. It means that you can get this high burst of power while running it at its full speed.
However, in that case, it will be noisier than it used to be. So in my suggestion, use routers for woodworking and cutting thin metal workpieces, which require low power for machining.
Spindles are high-power devices and advertised with a "root mean square" power rating. It means that you can take advantage of rated power throughout their continuous running.
So, you can consider spindles specifically for CNC machining applications for long durations without losing precision.
If you are looking for a spindle for hobby use or engraving and carving wood, a DC spindle is probably what you want.
You can consider AC spindles, which offer a wide speed range and handle different types of tools to cut high tensile materials.
For businesses looking to shave off seconds off their production process, ATC CNC spindles make perfect sense.
However they cost thousands of dollars, and can sometimes cost as much as the CNC machine itself.
Size and Build
Usually, routers have a 65mm outer diameter that lets them fit into router mount, which comes as standard with most CNC routers.
Their body is made of aluminum, which makes them lightweight to be moved by even NEMA 17 stepper motors.
Spindles have steel or cast iron construction because they are designed for heavy-duty CNC machining.
Their solid construction makes them heavy, so the motors of your CNC router should be powerful enough to handle the weight of spindles.
The weight of the cutting head that can be used is limited in most CNC routers under $5k.
Typically most popular hobby-grade CNCs like Shapeoko, X-Carve, Onefinity, and Workbee use a router instead of a spindle for this very reason.
A heavy spindle is difficult to move around.
In addition, to support the power of a heavy spindle, you need additional reinforcement in your Z-axis.
The frame of the CNC should also be rigid enough to withstand the power generated by a VFD spindle.
Consider these limitations carefully before upgrading your CNC from a router to a VFD spindle.
Routers are consumer-grade devices, handy, and can be used by anyone. If you are a beginner or hobbyist, you can prefer router over spindle due to their simple plug-and-play design to getting started with CNC machining.
Spindles are advanced cutting tools and designed for professional use. If you are running an industry, you can leverage the advantage of their long operation cycle for woodworking and metal machining without too much overheating.
If your project requires multiple tool changes, you can consider an automatic tool changer spindle, which can reduce cycle time and speed-up production.
However, setting up the spindle may be a bit complex and requires some skills like, to power the spindle, you need to connect a three-phase supply to the VFD.
Lifespan and durability
The lifespan of routers and spindles is calculated at around 80% of maximum rated loading. Spindles have a maximum lifespan of 12,000 hours, and they can be doubled or triple if run under low load conditions.
If you do a lot of heavy-duty CNC machining, you should consider spindles because you can push them hard for continuous production.
If you use a CNC router occasionally or for a short period, routers will give you good value for money.
You can't push routers hard as it can break them down before 1,200 hours, which is usually the lifespan of routers. If you do so, their bearings will wear out and need to be replaced.
While routers use brush-type motors that make them noisy, spindles use brushless motors that make them quiet, reduce their maintenance cycle and make them durable than routers.
Cost and warranty
If you are on a budget or looking to do woodworking primarily, routers are a perfectly acceptable choice.
They are inexpensive and can be replaced easily.
For beginners, routers have a much easier learning curve compared to spindles when getting started with CNC work.
You can also consider routers for low project demands, which don't require continuous operation.
Additionally, all routers have a one-year service warranty, which is also a good advantage.
Spindles are fast and are usually much costlier than routers but can run for longer durations than routers and are designed for heavy-duty CNC machining.
Although spindles are advanced, offer lots of features and high speeds, it becomes more expensive to repair them. Hence, you need to perform regular maintenance for optimum performance.
Mostly, all spindles are covered under a one-year warranty from the shipment date, which is also a good thing.
If you are a beginner or hobbyist and if you're not confident about the electrical wiring required for a VFD, then choosing a router might be the way to go.
Bosch, DeWalt, and Makita are the commonly used router brands for CNC work.
Each one is available with a slightly different-sized mount and is generally cheaper than a spindle.
Spindles are the apt choice for CNC machines requiring heavy use.
However, their setup complexity and cost can be off-putting to many.
Routers and spindles have their unique benefits as well as downsides.
To make a good choice between a router and a spindle, consider each factor discussed above and make a calculated choice.
The following two guides will help you choose the spindle or router you need for your CNC.
Frequently asked Questions (FAQ)
Can I use end mill in a router to cut wood?
End mills can be used in a router to cut wood if they are carefully chosen. However, it's not ideal. Consider the flutes of the end mill first because, for woodworking, less is good. Ideally, you should go with two flute end mill. Unlike routers, spindles have ER20 collet, which lets you use end mills of various sizes.
More can be found here- End Mill vs Router Bit